The present invention relates to a laser optical touch control module, an analog-to-digital conversion system and a method of the same, especially to the laser optical touch control module formed by a light emitting part with a laser light source and a light receiving part with a position sensor. Light paths of the light emitting part and the light receiving part are in parallel or share the same light path with each other. A variable reference level generator calculates to generate a variable reference level according to a peak value of output signal of the position sensor, and/or a reference voltage level (VB), and/or a variance of temperature, light source intensity, ambient light intensity etc. Then the output data of the sensor is effectively and quickly converted into a digital signal base on the variable reference level by a level comparator and the digital signal is output.
Instead of buttons used for control of general monitors, various functions of touch control displays most popular now such as pointing and selecting, image switching, or zoom out/in, etc are performed through a touch control widget such as fingers or touch control pen directly in contact with surface of the display. The touch control displays available now include many different systems such as resistive type, capacitive type, Surface Acoustic Wave (SAw) type, Infrared (IR) type, optical imaging type, etc. Each has its own advantages and shortcomings. For example, the optical imaging type can be applied to large-scale displays with cost-effectiveness between SAW type and capacitive type. The display has good transparency (up to 100%) and good resolution. The shortcomings include no applications to small-size panel (<15″). Moreover, it's easy to be affected by ambient light so that additional light sources, and reflective strips or light absorbing strips are required.
Refer to US Pat. App. Pub. No. 2009/0200453, U.S. Pat. Nos. 7,538,759, 7,692,625, 7,629,967, these are techniques available now related to optical touch control systems. Generally, at least one set light source such as LED light source is disposed on four edges or corners on surface of a rectangular display so as to light outer surface of the whole display. Moreover, four edges (frame) on surface of the display are arranged with reflective strips or light absorbing strips perpendicular to one another. At least two sets of position sensors (such as camera) with crossed sensing directions are disposed on edges on surface of the display. When a touch control device such as finger or touch control pen is in contact with surface of the display, the touch control device blocks light emitted to surface of the whole display or causes the light scattered. Through reflection of the reflective strips or absorption of the light absorbing strips, at least two sets of position sensors sensing position of the touch control device, one processing circuit with calculation function, the coordinate of the actual position of the touch control device on surface of the display is obtained. The functions of the optical touch control system are provided.
Most of optical touch control systems available now use LED (light-emitting diode) as light source. Yet LED light is not highly coherent light and the sensitivity of touch control is unable to be increased effectively. Moreover, the LED light source and the position sensor such as camera are separated from each other and used together with reflective strips or light absorbing strips set on certain positions around surface of the display. Thus the structure is complicated and the cost is high. Especially the light provided by the LED light source is usually visible light, it's easy to be interfered or affected by ambient visible light. Thus detection sensitivity of the position sensor of the optical touch control system is reduced. That means signal/noise ratio (SNR) is reduced and signal interpretation is further affected. Therefore efficiency of the optical touch control system is reduced.
Refer to FIG. 1, FIG. 1A, FIG. 8 and FIG. 8A, at least one light source 11 (10) such as LED or laser is arranged at four corners or four sides of a frame on surface of a rectangular display 2 so as to light surface of the whole display. That means a light or linear light emitted area (so-called light screen) is formed on surface of the display 2. Moreover, reflective strips or light absorbing strips perpendicular to one another (not shown in figure) are disposed around the edges on surface of a display 2. At least two sets of position (image) sensor 21 (there is only one in figure) with crossed sensing directions are set on edges around surface of the display 2. When a touch control device 3 such as finger or touch control pan touches surface of the display, the touch control device 3 causes scattering of light emitted on surface of the whole display 2 (reflective type as shown in FIG. 1) or blocks the light (photo interrupter type as shown in FIG. 8). Now through reflection of the reflective strips or absorption of the light absorbing strips, the reflective or blocked laser beam due to the touch control device 3 as shown in FIG. 1 and FIG. 8 acts on an axis of active pixels of the position (image) sensor 21 to for a signal output/sensor output data, represented by Vout as shown in FIG. 1A and FIG. 8A.
A relative position of the touch control device 3 in least two directions is detected by at least two sets of position sensors. Then through one processor or processing circuit with calculation function, the coordinate of the actual position of the touch control device 3 on surface of the display 2 is obtained. The functions of the optical touch control system are provided. Moreover, the sensor output data Vout from the position (image) sensor 21 shown in FIG. 1A and FIG. 8A is analog data. The analog data should be converted into digital data first so as to be processed by a processor such as MCU (Micro Control Unit), CPU (Central Processing Unit) or DSP (Digital Signal Processing), but not limited to the above processors for obtaining the coordinate of the actual position of the touch control device 3 on surface of the display 2.
However, the conversion of the sensor output data Vout into digital data mentioned above is usually performed by an analog-to-digital conversion (ADC) circuit, as prior arts revealed in U.S. Pat. No. 4,839,739, US Pub. No. US2009/0190944 and US2010/0171853. But the installation cost of the ADC circuit is quite high and the ADC circuit also increases loading of the processor. Thus the program efficiency is reduced. Moreover, the operation conditions of the optical touch control system in use always changes along with the environment outside and component properties. This is called variance such as sensor element variance, temperature variance, light source intensity variance, ambient light intensity variance, etc. This lead to upward or downward variation of basic voltage level of the sensor output data Vout from the position (image) sensor 21. For example, the changes of the sensor output data Vout from a solid line to a dotted line shown in FIG. 1A and FIG. 8A increase the loading of the processor and reduce the program efficiency. The above shortcomings have negative effects on development and prevalence of the analog-to-digital conversion circuit system with the position (image) sensor signal or the optical touch control system.
Thus there is room for improvement in the fields of optical touch control system and the analog-to-digital conversion circuit system with the position (image) sensor signal and a need to develop a new optical touch control system and a novel analog-to-digital conversion circuit system. The new optical touch control system has simple structure, reduced cost but having no reflective strips/or or light absorbing strips while the novel analog-to-digital conversion circuit system has reduced cost, less loading of the processor program, and increased program efficiency but without the use of ADC circuit.